Soaking pit furnace

ABSTRACT

A soaking pit furnace used for preparing metal ingots or blooms is provided with two sets of heating means, a principal burner means and an auxiliary burner means mounted in the upper portion of one wall of the furnace. The furnace also has an evacuating means in the lower portion of the same wall. The auxiliary heating means can supply only a minor portion of the heat requirement, but is capable of injecting hot gases into the furnace enclosure at a velocity of at least 70 meters per second.

United States Patent Knaak 1 June 27, 1972 SOAKING PIT FURNACE [56]Relerenees Cited [72) inventor: Rudiger Kneak, Neuss. Germany UNITEDSTATES PATENTS [73] Assignee: Koppers-Wistra-Olenbau Geeellschalt mit3,198,855 8/1965 Suydam 263/40 X beschrenkter Heftung, Dusseldorf. Ger-2,638,334 5/1953 Jones ...263/52 X many 2,849,221 8/1958 Cone et al..263/43 [22] Filed: Sept. 16, i970 Primary Examiner-John J. CambyAttorney-Michael S. Striker [2i] Appl. No.: 72,772

[57] ABSTRACT [30] Foreign Application Priority Data A soaking pitfurnace used for preparing metal ingots or blooms is provided with twosets of heating means, a principal Sept Germany 19 47 391? burner meansand an auxiliary burner means mounted in the upper portion of one wallof the furnace. The furnace also has [52] [1.5. CI. ..263/40 R, 263/52an evacuating means in the lower portion of the same wall. [5] Int. Cl..F27b 3/02 The auxiliary heating means can supply only a minor portion58 Field of Search ..263/40, 43, 52 of the heat requirement. but iscapable of injecting hot gases into the furnace enclosure at a velocityof at least 70 meters per second.

13 Claims, 2 Drawing Figures SOAKING PIT FURNACE BACKGROUND OF THEINVENTION A substantial proportion of the metallurgical soaking pitfurnaces used for heating or temperature equilibration of steel ingotsor blooms are of the so-called one-way soaking pit type. In this type ofconstruction, one or more burners are positioned in the front wall ofthe oven chamber and a vent is also positioned in the front wallunderneath the burners. This design leads to low-cost construction andrelatively low requirement for space. In view of the large number ofoven chambers required for the manufacture of steel, these arefrequently decisive factors.

Despite the cited advantages of the one-way soaking pit, it yields onlyincomplete temperature equilibration in steel ingots. This is a seriousdifficulty because large temperature differences within a workpiece areunfavorable to the rolling process. Moreover, since there is a minimumtemperature which all parts of the ingot must exceed, then the greaterthe temperature differences in the ingot, the higher the temperature ofthe hottest portion. Excessively high temperatures cause strong scaling,operating difficulties, and an economic loss due to a drop in the outputof steel.

Blocks to be heated are generally placed vertically in the heatingchamber. Temperature differences occur most frequently between the topsand bottoms of the pieces. Metallurgists refer to this temperaturedifference as being between the head and the foot of the ingot.Temperature differences also occur between opposite faces of the blockswhere the face turned toward the source of heat is hotter than theopposite face. Bringing all parts of the ingot to a uniform temperatureis rendered more difficult by the fact that the blocks may be introducedcold as well as hot.

The temperature of the blocks must be raised rapidly which requires thata large source of heat be used. For temperature equilibration the rateof heat introduction into the chamber need only be about l percent ofthe full capacity of the source of heat. Since, usually, the blocks arehot when introduced into the heating chamber, the rate of heat inputinto the chamber need only be to percent of the full capacity of theheat source for the most part, and performance during equilibrating theblocks is crucial.

The more uniformly the workpiece is heated, the shorter will be thedwell time in the chamber. Furthermore, heat consumption will be reducedand the output capacity of the system will be increased.

Attempts have been made to improve the heating process in specificdirections. Operating according to conventional methods, one or moreburners are used, and these are cycled between high and low heat outputsdepending on the heat requirement of the system. As is known, the nextimprovement of this technique consisted of using two or more burnersarranged on a front wall of a heating chamber which were shut off insequence as the head load decreased. In this way the system could beheld within a narrower range of temperatures. It was possible to arrangethe burners so that the length of the flame, the burning characteristicsand the velocity of discharge of the burners could be controlled.Nevertheless, the results achieved by operating as described have provedto be inadequate. At all times uniform and constant regulation isnecessary, dwell times in the chambers are too long, and temperaturedifferences are too large.

SUMMARY OF THE INVENTION It is an object of the invention to provide asoaking pit furnace for heating ingots and blooms to a temperaturesuitable for further processing, while avoiding substantial temperaturedifferences between different parts of a workpiece.

It is a further object to lower the maximum temperature to which anypart of any workpiece is heated while making certain that every part ofevery workpiece reaches a specific minimum temperature.

It is yet another object to decrease the dwell time of workpieces in thefurnace and thereby increase the output per unit of time by the furnace.

It is still another object to provide a method of operating the burnersin the soaking pit furnace to achieve the above objects.

Applicant has found that the process of heating up ingots or blooms in asoaking pit furnace can be improved by placing several burners in thefront wall of the furnace and controlling these in response to thedemand. When the demand is low, only one or two of the burners are putinto operation; as the demand increases, more burners are used to supplythe heat. This technique is distinguished by the fact that at lowdemands, the one or two burners used to supply the heat should becapable of supplying not more than 20 percent of the maximum output ofall burners operating together.

Moreover, the gas velocity at the orifices or nozzles of the one or twoburners should be more than 70 meters per second at full load. This typeof arrangement is desirable because the workpieces are generally putinto the furnace while hot and consequently the required burner load forthe final phases of the heating process is apt to be 20 percent or less.It is consequently advantageous to arrange to have one or two specialburners with the characteristics defined above. These special burnersmay be termed the auxiliary burners or heat-producing means, while theburner which they flank and which produces from to 95 percent of thetotal heat requirement may be termed the principal burner orheat-producing means.

The auxiliary burner or burners have a function in addition to supplyingup to 20 percent of the total heat requirement: this is to causeturbulence in the chamber gases, this turbulence being largelyresponsible for the excellent temperature equilibration achieved in thefurnace, according to the invention. The gas emerging from the auxiliaryburner to burners at 70 m/sec. causes turbulence by entraining theatmosphere of the furnace. Gas velocities higher than m/sec. can beachieved by burning the gases of the auxiliary burner or burners in anauxiliary chamber and leading the combustion products into the furnacechamber.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a horizontal sectionthrough the furnace chamber; and

FIG. 2 is a vertical section through the line I-I.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows a rectangularsoaking pit furnace 1 having a front wall la, a principal burner 2flanked by auxiliary burners 3 and a back wall 5. The billets aredesignated by the reference numeral 4.

FIG. 2 is a vertical section along the line II. This Figure shows thelocation of the evacuating means 6 through which the gas in the chambervents. The Figure also indicates the direction of flow of the gas asshown by the arrows. As the Figure shows, gas enters the furnace throughthe burners, travels for the most part across the tops of the workpiecesto the back wall 5 where it is deflected downward, and then travelsacross the bottom of the furnace leaving through the vent 6. Though thegeneral course of the gaseous combustion product is as shown in FIG. 2,it will be realized that considerable mixing takes place as a result ofthe injection of combustion products from burners 3 at high velocity. Itfollows then that the hot, high velocity combustion gases do not travelmerely once across the top of the billets where they give up part oftheir heat and once across the bottom after reflection from the backwall 5, but that the gases actually make many passes across theworkpieces as a result of entrainment of the chamber atmosphere by thehigh velocity gases from the auxiliary heating means.

To achieve the above results, it is necessary that the streams from theburners be emitted with the highest possible velocity. As a firstapproximation, considering the auxiliary burners as free jets, then thevelocity at each point in the stream is proportional to the orificevelocity and the orifice diameter. The quantity of heating mediumentering the chamber per unit of time, and thereby the quantity of heatintroduced, is proportional to the product of the orifice velocity andthe square of the orifice diameter. More exact investigation has shownthat the stream velocity at any random point in the stream isproportional to the root of the orifice velocity for equal volumesissuing from the orifice that is, for equal input. These considerationsshow that for efiective circulation of the gases in the furnace, theorifice cross section should be small and the velocity at which the gasstream issues, should be high. It can be stated that the higher thestream velocity of the auxiliary burners, the greater will be the effectand the better will be the circulation. Further investigation of thiseffect has shown that if the auxiliary burner or burners supply no morethan percent of the maximum requirements, then the burners can beoperated at full load continuously and any decrease in the streamvelocity can thereby be avoided.

It has been found that by using a high velocity burner with its owncombustion chamber, it becomes possible to introduce the combustionproducts therefrom at a velocity of 90 m/sec. into the soaking pitfurnace chamber. This rate is substantially above that possible when theauxiliary burners are mounted in the front wall la on the furnacechamber. It is therefore a particularly favorable mode of constructionand operation.

It is an especially favorable construction to locate the principalburner in the upper part of the front wall In and centrally with respectto side walls. This principal burner should supply from 85 to 90 percentof the total load. Two auxiliary burners are located at the same levelas the principal burner and flank the principal burner on either side.

The auxiliary burners are so constructed that after the initial portionof the heating where the maximum heat input is required, and the heatrequirements decrease, that the auxiliary burners can be throttled down.Initially the burners are run at a constant setting and after reachingsome minimum level, they are operated on an otT-on mode. In this way,the opera tion of these burners at a rate lower than the minimum atwhich they can give satisfactory performance is avoided.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of eq uivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. In a metallurgical furnace, particularly in a soaking pit, a

combination comprising wall means defining an enclosure having a portionfor reception of a charge; at least one principal and a plurality ofauxiliary heating means provided in the region of said wall means fordischarging hot gases into said enclosure at a total maximum heatingcapacity of 100 percent, the combined maximum heating capacity of saidplurality of auxiliary heating means being at most equal to 20 percentof the total heating capacity of all of said heating means, and each ofsaid plurality of auxiliary heating means being arranged to dischargehot gases into said enclosure at a velocity of at least 70 meters persecond when operated at its maximum heating capacity.

2. A combination as defined in claim 1, wherein each of said heatingmeans comprises at least one fuel hunter.

3. A combination as defined in claim I, wherein at least one of saidauxiliary heating means comprises a high velocity burner having acombustion chamber provided with at least one orifice for discharge ofhot combustion products into said enclosure at a velocity of at least 90m/sec.

4. A combination as defined in claim 1, wherein the heating capacity ofsaid auxiliary heating means at least approximates 10 percent of thetotal heating capacity of all of said heating means.

5. A combination as defined in claim 1, wherein the heat energy outputof said auxiliary heating means is constant.

6. A combination as defined in claim 1, wherein said principal heatingmeans comprises at least one fuel burner whose heating capacityconstitutes between and percent of the total capacity of said heatingmeans.

7. A combination as defined in claim 1, wherein said auxiliary heatingmeans comprises two fuel burners flanking said principal heating means.

8. A combination as defined in claim 1, wherein the heat energy outputof at least one of said heating means is variable.

9. Process of bringing metal workpieces to a required high temperatureby means of hot gases, comprising the steps of placing said workpiecesin an enclosure; introducing into a first region in said enclosure hotgases in such quantity that such gases supply at least 80 percent of therequired heat energy; and introducing into a plurality of additionalregions of said enclosure hot gases at a velocity of at least 70 m/sec,whereby the gases introduced at said additional regions supply theremaining heat energy required.

10. Process as defined in claim 9, wherein said hot gases introduced atsaid additional regions supply up to 10 percent of the heat energyrequired.

11. Process as defined in claim 9, wherein said hot gases introduced atsaid additional regions enter said enclosure at a velocity of at least90 m/sec.

12. Process as defined in claim 9, further comprising the steps ofgradually reducing the rate of introduction of hot gases at at least oneof said regions when the temperature within said enclosure rises to apredetermined value; and thereupon maintaining constant the rateofintroduction of hot gases at said regions.

13. Process as defined in claim 12, further comprising the step ofintermittently interrupting the introduction of hot gases at saidregions.

1. In a metallurgical furnace, particularly in a soaking pit, acombination comprising wall means defining an enclosure having a portionfor reception of a charge; at least one principal and a plurality ofauxiliary heating means provided in the region of said wall means fordischarging hot gases into said enclosure at a total maximum heatingcapacity of 100 percent, the combined maximum heating capacity of saidplurality of auxiliary heating means being at most equal to 20 percentof the total heating capacity of all of said heating means, and each ofsaid plurality of auxiliary heating means being arranged to dischargehot gases into said enclosure at a velocity of at least 70 meters persecond when operated at its maximum heating capacity.
 2. A combinationas defined in claim 1, wherein each of said heating means comprises atleast one fuel burner.
 3. A combination as defined in claim 1, whereinat least one of said auxiliary heating means comprises a high velocityburner having a combustion chamber provided with at least one orificefor discharge of hot combustion products into said enclosure at avelocity of at least 90 m/sec.
 4. A combination as defined in claim 1,wherein the heating capacity of said auxiliary heating means at leastapproximates 10 percent of the total heating capacity of all of saidheating means.
 5. A combination as defined in claim 1, wherein the heatenergy output of said auxiliary heating means is constant.
 6. Acombination as defined in claim 1, wherein said principal heating meanscomprises at least one fuel burner whose heating capacity constitutesbetween 85 and 90 percent of the total capacity of said heating means.7. A combination as defined in claim 1, wherein said auxiliary heatingmeans comprises two fuel burners flanking said principal heating means.8. A combination as defined in claim 1, wherein the heat energy outputof at least one of said heating means is variable.
 9. Process ofbringing metal workpieces to a required high temperature by means of hotgases, comprising the steps of placing said workpieces in an enclosure;introducing into a first region in said enclosure hot gases in suchquantity that such gases supply at least 80 percent of the required heatenergy; and introducing into a plurality of additional regions of saidenclosure hot gases at a velocity of at least 70 m/sec., whereby thegases introduced at said additional regions supply the remaining heatenergy required.
 10. Process as defined in claim 9, wherein said hotgases introduced at said additional regions supply up to 10 percent ofthe heat energy required.
 11. Process as defined in claim 9, whereinsaid hot gases introduced at said additional regions enter saidenclosure at a velocity of at least 90 m/sec.
 12. Process as defined inclaim 9, further comprising the steps of gradually reducing the rate ofintroduction of hot gases at at least one of said regions when thetemperature within said enclosure rises to a predetermined value; andthereupon maintaining constant the rate of introduction of hot gases atsaid regions.
 13. Process as defined in claim 12, further comprising thestep of intermittently interrupting the introduction of hot gases atsaid regions.